The mode command is entered on a master controller. This command is used to enable and configure control mode and observe mode settings and is used to configure passive monitoring and active monitoring. A prefix can be monitored both passively and actively.
Observe mode monitoring is enabled by default. In observe mode, the master controller monitors prefixes and exit links based on default and user-defined policies and then reports the status of the network and the decisions that should be made but does not implement any changes. This mode allows you to verify the effectiveness of this feature before it is actively deployed.
In control mode, the master controller coordinates information from the border routers and makes policy decisions just as it does in observe mode. The master controller monitors prefixes and exits based on default and user-defined policies but then implements changes to optimize prefixes and to select the best exit. In this mode, the master controller gathers performance statistics from the border routers and then transmits commands to the border routers to alter routing as necessary in the OER managed network.
The master controller passively monitors IP prefixes and TCP traffic flows. Passive monitoring is configured on the master controller. Monitoring statistics are gathered on the border routers and then reported back to the master controller. OER uses NetFlow to collect and aggregate passive monitoring statistics on a per prefix basis. No explicit NetFlow configuration is required. NetFlow support is enabled by default when passive monitoring is enabled. OER uses passive monitoring to measure the following information:
Delay --OER measures the average delay of TCP flows for a prefix. Delay is the measurement of the time between the transmission of a TCP synchronization message and receipt of the TCP acknowledgment.
Packet Loss --OER measures packet loss by tracking TCP sequence numbers for each TCP flow. OER estimates packet loss by tracking the highest TCP sequence number. If a subsequent packet is received with a lower sequence number, OER increments the packet loss counter.
Reachability --OER measures reachability by tracking TCP synchronization messages that have been sent repeatedly without receiving a TCP acknowledgment.
Throughput --OER measures outbound throughput for optimized prefixes. Throughput is measured in bits per second (bps).
OER passively monitors TCP traffic flows for IP traffic. Passive monitoring of non-TCP sessions is not supported.
OER uses Cisco IOS IP Service Level Agreements (SLAs) to enable active monitoring. IP SLAs support is enabled by default. IP SLAs support allows OER to be configured to send active probes to target IP addresses to measure the jitter and delay, determining if a prefix is out-of-policy and if the best exit is selected. The border router collects these performance statistics from the active probe and transmits this information to the master controller. The master controller uses this information to optimize the prefix and select the best available exit based on default and user-defined policies. The active-probe command is used to create an active probe.
In Cisco IOS Release 12.4(15)T the throughput keyword was added to enable the throughput data from passive mode monitoring to be considered when optimizing UDP traffic for both performance and load balancing. UDP traffic can be optimized only for performance (for example, delay, jitter, and loss) when active monitoring data is available. To enable load balancing of UDP traffic, throughput data from passive monitoring is required.
Fast Failover Monitoring
In Cisco IOS Release 12.4(15)T, a new monitoring mode, fast monitoring, was introduced. Fast monitoring sets the active probes to continuously monitor all the exits (probe-all), and passive monitoring is enabled too. Fast failover monitoring can be used with all types of active probes: ICMP echo, Jitter, TCP connection, and UDP echo. When the mode monitor fast command is enabled, the probe frequency can be set to a lower frequency than for other monitoring modes, to allow a faster failover ability. Under fast monitoring with a lower probe frequency, route changes can be performed within 3 seconds of an out-of-policy situation. When an exit becomes OOP under fast monitoring, the select best exit is operational and the routes from the OOP exit are moved to the best in-policy exit. Fast monitoring is a very aggressive mode that incurs a lot of overhead with the continuous probing. We recommend that you use fast monitoring only for performance sensitive traffic.
Optimal Exit Link Selection
The master controller can be configured to select a new exit for an out-of-policy prefix based on performance or policy. You can configure the master controller to select the first in-policy exit by entering the good keyword, or you can configure the master controller to select the best exit with the best keyword. If the good keyword is used and there is no in-policy exit, the prefix is uncontrolled.
The following example enables both active and passive monitoring:
Router(config)# oer masterRouter(config-oer-mc)# mode monitor both
The following example enables fast failover monitoring:
Router(config)# oer masterRouter(config-oer-mc)# mode monitor fast
The following example configures the master controller to enable active monitoring with throughput data from passive monitoring:
Router(config)# oer masterRouter(config-oer-mc)# mode monitor active throughput
The following example enables control mode:
Router(config)# oer masterRouter(config-oer-mc)# mode route control
The following example configures the master controller to enable control mode and to enable EIGRP route control that applies a community value of 700 to EIGRP routes under OER control:
Router(config)# oer masterRouter(config-oer-mc)# mode route controlRouter(config-oer-mc)# mode route metric eigrp tag 700
The following example configures the master controller to select the first in-policy exit:
Router(config)# oer masterRouter(config-oer-mc)# mode select-exit good